Dietary protein counting as an alternative way of maintaining metabolic control in phenylketonuria

Abstract

Objective: To compare a gram protein exchange system (1g=50-mg Phenylalanine) with a unit exchange system (1unit=15-mg Phenylalanine) and its effect on the blood Phenylalanine (Phe) levels and acceptance in the dietary management for children and adolescents with Phenylketonuria. Methods: In Phase One, participants were randomised to continue counting Phe unit exchanges (n=8) or changed to counting gram protein exchanges (n=10), using a new diet chart developed in-house. Foods containing less than 20mg Phe per serve were now considered “free.” Interim data analysis confirmed no significant deterioration in Phe levels of the study group and the control group was changed to protein counting. In Phase Two, 18 participants were educated to use an updated version of the in-house diet chart – in this version foods containing less than 50mg Phe per serve were considered “free.” In both phases, attitudes to PKU and its management were evaluated at baseline and 6months. Phenylalanine and tyrosine levels were measured from filter paper blood spots by tandem mass spectrometry. Results: Phase One: Phe levels over 6months were comparable to pre-study levels (mean Phe pre 366μmol/L+/− 169, mean Phe post change=388μmol/L+/− 160). Phase Two: Four participants had a significant improvement in blood Phe levels, nine showed no significant change and one participant’s levels were significantly higher. There was incomplete data on four participants. All participants preferred the freer diet chart. Conclusion: Protein exchanges (foods containing less than 50mg Phe/serve uncounted) are an alternative method of measuring Phe intake in the dietary management of Phenylketonuria.